Blast shelter
A typical specification for heavy civil defence shelter in Europe during the Cold war was an overhead explosion of a 500 kiloton weapon at the height of 500 meters.
[citation needed] However, in the countryside or in a suburb, the likely distance to the explosion is much larger, as it is improbable that anyone would waste an expensive nuclear device on such targets.
The most common purpose-built structure is a steel-reinforced concrete vault or arch buried or located in the basement of a house.
Most expedient blast shelters are civil engineering structures that contain large buried tubes or pipes such as sewage or rapid transit tunnels.
Even these, nonetheless, require several additions to serve properly: blast doors, air-filtration and ventilation equipment, secondary exits, and air-proofing.
Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and prompt radiation.
Bunkers designed for large ground shocks must have sprung internal buildings, hammocks, or bean-bag chairs to protect inhabitants from the walls and floors.
In bunkers inhabited for prolonged periods, large amounts of ventilation or air-conditioning must be provided to prevent heat prostration.
In bunkers designed for war-time use, manually operated ventilators must be provided because supplies of electricity or gas are unreliable.
Bunkers must also protect the inhabitants from normal weather, including rain, summer heat and winter cold.
Thick (5-mil or 125 μm), inexpensive polyethylene film serves quite well, because the overburden protects it from degradation by wind and sunlight.
When a house is purpose-built with a blast shelter, the normal location is a reinforced below-grade bathroom with large cabinets.
[citation needed] In apartment houses, the shelter may double as storage space, as long as it can be swiftly emptied for its primary use.
In the second half of the 20th century, metro stations in eastern Europe and the USSR were constructed to serve as blast shelters.
